timer_freq.QuadPart /= 1000; // To convert frequency from 'ticks per second' to 'ticks per millisecond'

Timer frequency is usually in the range of millions, but there's _nothing_ to prevent Microsoft from changing it to a value that's in the thousands. Or whatever they please, that's why win32 QueryPerformanceFrequency [1] API call exists in the first place! That would break any code with this "fix".

It also reduces accuracy — a second might no longer be 1000 ms, but maybe 1001 ms.

I think a better fix would be either to simply use doubles instead of floats or to at least offset the value to start of game — as long as a single game can't last months.

Values are already offset (in noted snippet, timer_begin is approx. the time process has started, as in - queried during initialization).

While I'll defend the idea of modifying QueryPerformanceFrequency result to achieve desired resolution (in this case, ticks per ms), you are absolutely right about the possibility of the value becoming several orders of magnitude smaller in the future. In this case multiplying the subtraction result by 1000 instead of dividing frequency is indeed far safer.

> While I'll defend the idea of modifying QueryPerformanceFrequency result to achieve desired resolution (in this case, ticks per ms)

Did a quick back-of-the-envelope calculation, and the suggested solution is off by 42 milliseconds per minute on a hypothetical 3 GHz system. It might not sound like much (~2.5 frames at 60 fps), but I've seen smaller errors cause massive issues when it comes to time.

It's better to do it right rather than to later on debug these often surprising issues we didn't have sufficient imagination for.

Unless one is looking for an amazing bug hunting war story, of course. :)

And as for returning the result - original code does return a float, so while I could also return a double it probably wouldn't make any difference, as I expect the game to store those results in floats too. Moreover, since the result is basically "session time", it is expected to last up to several hours - in which case floats are still fine.

Either way, it may indeed be beneficial to return time as a double - so code which stores it in floats will not care about the change, but the code which uses it in intermediate calculations will and it will potentially benefit from it. Notes taken!

EDIT:
Will generate more code warnings of course, but I believe it's a good tradeoff, since the game has a ton of them anyway and going through them all is something for another day.

Well, there's always the other side as well: if the value is in the billions, it'll degenerate back to the original bug.

On single CPU socket systems, Windows seems to usually compute QueryPerformanceCounter by simply shifting CPU RDTSC count right by 10 bits, effectively dividing the value by 1024. So exactly 3.0 GHz system would have 2929687 in QueryPerformanceFrequency return value.

On NUMA machines instead of RDTSC QueryPerformanceCounter uses HPET or APIC or whatever is available, because RDTSC is not HW synchronized between CPU sockets. I bet those HPET divisors will be in different divisor range.

No matter what clock source Windows might use, simply using doubles would have fixed the issue. No point to use floats in the first place.

rationals might be a better solution since they could use whatever divisor they want without throwing away precision. I'm not very familiar with MS apis but if they provide some facility for telling you how many 'ticks' there are per second you could use that to generate the divisor as well.

There is. To save people the click, there's a pair of functions - QueryPerformanceCounter and QueryPerformanceFrequency. QPC gives you ticks, QPF gives you ticks per second, so QPC / QPF is the rational you seek.

You actually don't need to use Detour hacks to fake QueryPerformanceCounter, this is built into Application Verifier as a check called "TimeRollOver". If you're writing Windows apps or games, it's highly recommended to try to run your app through AppVerifier, it'll catch lots of mistakes by turning all of the super permissive Win32 APIs into super vicious strict versions that try to find mistakes in your code.

Windows CE has a 32-bit uptime counter (GetTickCount()) that wraps after ~49 days, but on startup it sets the value so that it wraps around in three minutes, increasing the likelihood that overflow bugs will be sussed out during development. https://news.ycombinator.com/item?id=3231781

While it is not mentioned in the article, I am aware of /arch:IA32 (don't use SSE instructions) and I have tried it - no luck.

On the other hand, using /fp:fast with VS2017 did give me similar results to what VS2003/VS2010 produces - so if I were to guess, VS2003 generates x87 math in a manner similar to fast math, while precise math breaks it?

The epic Turbo Pascal Runtime Error 200 is similar. Turbo Pascal for DOS runtime sleeps by running a no-op loop some number of times. It figures out this number during startup, and it immediately crashes with division by zero if your computer is faster than a typical PC from the late nineties. http://wiki-errors.com/runtime-error-200-%E2%80%93-the-pasca...

Calculate mult and shift based on the timer frequency. The multiplication likely needs to be done with a 96 or 128 bit output. If shift is forced to be >= 64 (on a 64-bit machine), then the resulting assembly code is short and fast.

No modding community of note. It's the first game in a series that has three direct sequels, two spinoffs, and a crossover title that all run well on Steam. As much as I miss some things about that version of the game, the sequels are better in more than just playability on windows.

I'll just have to remember to reboot before I play my favorite version of Taokaka, when I get the urge.

shrug I would just try to represent it w/more precision. Maybe then you wouldn't even need the complexity of a floating point number.

If you're lucky, your compiler can generate 64/128-bit math for your target if there's no native registers/ALU that wide. If not, it's not exactly rocket surgery to do this yourself. Or in dire cases, use an arbitrary precision library.

As a workaround you simply approximate to a significant figure past any other values in your calculation. So in practice it doesn't really matter that there's no exact base-10 representation as a decimal because there's always an approximation that introduces no error.